1. Field of the Invention
The present invention relates to a method for producing a scintillator panel, radiation detection apparatus, radiation detection system and scintillator layer, which are applied to a medical diagnostic imaging apparatus, non-destructive inspection apparatus, analytical apparatus, and the like. In particular, the invention relates to a scintillator panel, radiation detection apparatus, radiation detection system, and method for producing the scintillator layer, which are used for x-ray photography and the like. Incidentally, in the present specification, the category of radiation also includes corpuscular rays such as x-rays, α-ray, β-ray, γ-rays, and the like. As a detector for detecting radiation, a flat panel detector (hereinafter, abbreviated as “FPD”) is known. This combines an optical detector two-dimensionally disposed with a photoelectric conversion element using amorphous silicon (hereinafter, abbreviated as “a-Si”) and a TFT element with a scintillator converting radiation into light of a waveband sensible by the photoelectric conversion element.
2. Description of the Related Art
Nowadays, as recent TFT technologies for liquid crystal displays and maintenance of information infrastructures have come to be well developed, a variety of FPDs have been proposed, and even in the field of medical diagnostic images, a large display area and digitalization have been achieved.
Such FPDs can instantaneously read a radiation image and instantaneously display it on a display unit. Further, since the image can be directly taken out as digital information, the FPD is characterized by easiness of handling such as storing, processing, or transferring data. Further, though various characteristics such as sensitivity depend on imaging conditions, as compared with a conventional screen film system imaging method and a computed radiographic imaging method, such characteristics are confirmed to be equal to or superior to these methods.
As a digital radiation detection apparatus used for the FPD, there is an apparatus combined with a photoelectric detector which takes a phosphor that converts radiation into visible light and the like as a phosphor layer (scintillator layer) made of cesium iodide (hereinafter, referred to as “CsI”) in which a crystal grows columnar. To increase sensitivity of such radiation detection apparatus, an activator such as thallium (Tl) and sodium (Na) is added to the CsI of the phosphor layer. As compared with phosphor layers containing conventional particulate crystal phosphors, sensitivity and sharpness are dramatically improved.
International Publication No. WO98/36290 discloses a radiation detection apparatus used in such an FPD.
FIG. 5B of IEEE TRANSACTION ON NUCLEAR SCIENCE Vol. 37, No. 2, April 1990, p. 177-182, discloses that an increase in the concentration of an activator Tl increases the light-emission quantity, and with a certain concentration or more, the light-emission quantity is saturated.
On the other hand, though not using the scintillator layer to convert radiation into direct light, Japanese Patent Application Laid-Open No. 2003-50298 discloses a radiation image conversion panel using an accumulative phosphor.
The phosphor layer includes a layer made of a phosphor main ingredient component at a support medium side and a layer made of a phosphor component (main ingredient component and activator component) at a surface side, and a columnar crystal structure of each layer is formed by a vapor deposition method.
In Japanese Patent Application Laid-Open No. H10-223163, the scintillator layer is formed on a substrate surface of an x-ray image tube and a photoelectrode is formed on that layer. The scintillator is formed in two layers on a substrate, and the columnar diameter of the scintillator layer at an x-ray incident side is made smaller.
Japanese Patent Application Laid-Open No. 2002-31687 discloses a columnar crystal in which the scintillator layer is different in shape from a photosensor portion between the photosensor portion and a TFT portion.